Fix matplotlib sandboxing

This appears to fix plotting with matplotlib in python3.  This lets
things like //y2020/control_loops/python:finisher --plot work.

Change-Id: I8ff1c91cf078e3aa8b4d5660881c22c8de66f051
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/y2021_bot3/control_loops/python/BUILD b/y2021_bot3/control_loops/python/BUILD
index 7ade878..15dacaa 100644
--- a/y2021_bot3/control_loops/python/BUILD
+++ b/y2021_bot3/control_loops/python/BUILD
@@ -5,8 +5,10 @@
     srcs = [
         "drivetrain.py",
     ],
+    legacy_create_init = False,
     target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
+        ":python_init",
         "//external:python-gflags",
         "//external:python-glog",
         "//frc971/control_loops/python:drivetrain",
@@ -19,8 +21,10 @@
         "drivetrain.py",
         "polydrivetrain.py",
     ],
+    legacy_create_init = False,
     target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
+        ":python_init",
         "//external:python-gflags",
         "//external:python-glog",
         "//frc971/control_loops/python:polydrivetrain",
@@ -43,3 +47,11 @@
         "//frc971/control_loops/python:polydrivetrain",
     ],
 )
+
+py_library(
+    name = "python_init",
+    srcs = ["__init__.py"],
+    target_compatible_with = ["@platforms//os:linux"],
+    visibility = ["//visibility:public"],
+    deps = ["//y2020/control_loops:python_init"],
+)